In order to make synchronous circuits operate normally, it is necessary to generate a clock signal whose frequency is stable. By using a crystal oscillator, although a stable clock signal can be generated, it is difficult to generate a clock signal having a high frequency. On the other hand, oscillator circuits on a semiconductor integrated circuit can generate a clock signal having a frequency, while the frequency of the generated clock signal may be unstable due to variation of each of element and/or temperature characteristics.